Overrunning clutch

ABSTRACT

An overrunning clutch comprising a ratchet wheel ( 1 ) and a plurality of pawls ( 2 ) is disclosed. Each of the pawls ( 2 ) is rotationally supported on a disk member ( 5 ) by a shaft ( 3 ). The clutch is characterized by a permanent magnet ( 4 ) being fixed on the disk member ( 5 ) between the axes of the disk member ( 5 ) and the shaft ( 3 ) and facing the tail end of each pawl ( 2 ). Because each of the pawls are not driven by a spring in the clutch, the clutch could not be malfunction due to the fatigue failure of the spring in the case of frequent heavy load.

TECHNICAL FIELD

[0001] The present invention relates to an overrunning clutch, and moreparticularly, to a clutch that is in frequently overrunning conditionwith heavy load.

BACKGROUND ART

[0002] An inertial centrifugal ratchet is disclosed in Chinese UtilityModel patent CN91208227.5, wherein a magnetic ring is provided under theratchet. The pawls stretch radially outwardly in the direction effectedby the centrifugal force when gears are turning so as to mesh with theteeth of the ratchet. According to the technical solution disclosed inthe patent, the ratchet can't operate reliably when the pawls do notrotate flexibly, which is due to the centrifugal force that makes thepawls stretch radially outwardly to mesh with the teeth of the ratchet.

[0003] A US patent (U.S. Pat. No. 5,205,386) disclosed a pawl andratchet clutch with a pawl holdback means, wherein a magnet is disposedradially outwardly of associated pawl meshing end. The pawls stretchradially outwardly by the centrifugal force when the driving shaftrotates at a speed above a desired value. Once the pawl contacts withassociated magnet, it will be held by said magnet. Such clutch stillutilizes the spring force to drive pawl to swing and mesh with the teethof said ratchet. Therefore, the spring will be loaded frequently andrepeatedly in case of frequently overrunning condition with heavy load.The spring will be fatigue failure quickly and make the clutch bemalfunction. In addition, mechanical contact will take place between themagnet and the end of pawl of the clutch during operation, which makesthe two parts impinge each other frequently. Such contact andimpingement cause damage on magnet or make the magnet become hot. Theclutch could be malfunction when the magnet is damaged. The magnet willshrink when it is heated and then is relaxed, which will also make theclutch be malfunction.

DISCLOSURE OF INVENTION

[0004] The object of the present invention is to provide an overrunningclutch which doesn't need a spring to drive the pawl.

[0005] The present invention can achieve said object by providing a typeof overrunning clutch comprising a ratchet wheel and a plurality ofpawls. Each of the pawls is rotationally supported on a disk member by ashaft. A permanent magnet is fixed on the disk member between the axesof said disk member and said shaft and opposing to the tail end of eachpawl.

[0006] According to one preferred embodiment, such pawl includes aratchet end which engages with the ratchet teeth and a tail end awayfrom the ratchet end. A through hole for said shaft is provided betweenthe ratchet end and the tail end. The distance from the tip of theratchet end to the axis of the through hole is larger than that from thetip of the tail end to the axis of the through hole.

[0007] According to the present invention, the magnet is provided nearthe tail end of said pawl and between the axes of the disk member andthe shaft.

[0008] The distance from the tip of the ratchet end of the pawl to theaxis of the through hole is slightly larger than that from the tip ofthe tail end to the axis of the through hole. The ratio of the distancefrom the tip of the tail end to the axis of the through hole to thedistance from the tip of the ratchet end to the axis of the through holeis preferred to be 1:1.1.

[0009] According to another preferred embodiment of the presentinvention, the clutch further includes a mounting sleeve embedded insaid disk member. The permanent magnet is provided inside the saidmounting sleeve. The mounting sleeve is preferably made of non-magneticconduct materials, such as stainless steel, copper, aluminum, or thelike.

[0010] The permanent magnet is made of ferrite, preferably the materialof Neodymium-Fe-Boron. It is a cylinder, and the diameter of thecylinder is 16 mm and its height is 10 mm.

[0011] According to one preferred embodiment of the present invention,the distance between the tail end of said pawl and the permanent magnetis 1 mm when the ratchet end of said pawl engages with the ratchetteeth, the maximum distance between the tail end of said pawl and thepermanent magnet is 5 mm when the pawl disengages with the ratchetteeth.

[0012] This invention utilizes the magnetic force to make the pawl andthe ratchet engage with each other. Since no springs are applied, thereare no problems of fatigue failure. This will significantly extend theservice life of the clutch according to this invention in the case offrequently heavy load.

[0013] According to the present invention, the magnet will not contactwith the tail end of the pawl during operation. Such formation canensure that the magnet will not be impinged by the tail end of the pawlduring operation, which means that there is no force acting on itdirectly. Therefore, the magnet will not be worn or be damaged bymechanical force and it will not produce the problems of fatigue failureexisting in the prior art because there is no mechanical force acting onthe magnet directly. So the service life of the clutch according to thisinvention can be extended. On the other hand, since the magnet has thenature of shrinking when it is heated and expanding when it is cooled,the clearance between the magnet and the fixed means will be enlargedwhen the magnet is impinged by the mechanical force and produces heatduring operation. In such case the magnet will become loose. Accordingto this invention, there is no direct contact between the magnet and thetail end of the pawl, so the magnet will not become loose when beingheated. Such formation can ensure the magnet to operate for a long timeand can extend the service life of the clutch of this invention.

[0014] According to this invention, the distance from the tip of theratchet end of the pawl to the axis of the through hole is larger thanthat from the tip of the tail end to the axis of the through hole. Suchstructure can ensure the pawl to move reliably and be influenced by asmall magnetic force, therefore it can ensure the reliability of theclutch of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described through thespecific embodiments in connection with the accompanying drawings, inwhich:

[0016]FIG. 1 is a schematic view of the construction according to thisinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

[0017] The number 1 indicates a ratchet wheel in FIG. 1, the ratchetteeth 9 are provided on the inner side of the ratchet wheel 1. The diskmember 5 is coaxial with ratchet wheel 1 and can rotate relatively tothe ratchet wheel 1. A number of pawls 2 are shown in FIG. 1, thepractical number of the pawls can be determined according to the workingcondition. Each of the pawls 2 is rotationally supported on the diskmember 5 by a shaft 3. The pawl 2 is a long and thin element made offerromagnetism material such as steel. The pawl 2 includes a ratchet end6 which engages with the teeth of said ratchet wheel, and a tail end 7is opposing to the ratchet end 6. The distance a from the tip of theratchet end 6 to the center of the shaft 3 is larger than the distance bfrom the tip of the tail end 7 to the center of the shaft 3. In thisembodiment, a equals to 40 mm, b equals to 36 mm. The ratio of a/b canensure the pawl 2 to engage with ratchet teeth 9 on the ratchet wheel 1reliably under the action of the magnetic force of the magnet 4.

[0018] The magnet 4 is provided between the axes of the disk member 5and the axes of the shaft 3. Magnet 4 is near the tail end 7 of pawl 2.In this embodiment, the distance between the tail end 7 of said pawl 2and the magnet 4 is 1 mm when pawl 2 engages with the ratchet teeth 9,the maximum distance between the tail end 7 of said pawl 2 and themagnet 4 is 5 mm when pawl 2 disengages with the ratchet teeth 9. Theseclearances are ensured by the dimensions of respective elements andtheir relative position.

[0019] In this embodiment, the shape of magnet 4 is a cylinder and itsdiameter is 16 mm and its height is 10 mm. Magnet 4 is made of ferrite,preferably Neodymium-Fe-Boron. The pawl 2 is made of ferromagnetismmaterial, such as steel. Certainly, the shape of the magnet 4 can beother form, such as a rod with a rectangular cross-section and so on.

[0020] A mounting sleeve 10 is provided between magnet 4 and disk member5. The mounting sleeve 10 preferably is made of non-magnetic material,such as stainless steel, copper, aluminum, or the like. The usedmaterial can block effectively the path of the magnetic line of force toutilize the magnetic force of magnet 4 to the full extent and to drivethe pawl 2. In this embodiment, mounting sleeve 10 is just like a cup.The magnet 4 is placed into the mounting sleeve 10 from the upper openend thereof, then the mounting sleeve 10 and the magnet 4 are togetherbrought into a respective hole in the disk member 5. The mounting sleeve10 and the magnet 4 can be fixed in the disk member 5 through the methodof press-fit. Other ways can be utilized for said connection, forexample, the mounting sleeve 10 and the disk member 5 can be connectedtogether by threading or welding or the like.

1. A ratchet overrunning clutch comprising a ratchet wheel (1) and aplurality of pawls (2), each of the pawls (2) is rotationally supportedon a disk member (5) by a shaft (3), wherein a permanent magnet (4)being fixed on the disk member (5) between the axes of the disk member(5) and the shaft (3) of the pawl (2) and opposing to the tail end ofpawl (2).
 2. The clutch according to claim 1, wherein the pawl (2)includes a ratchet end (6) which engages with the teeth of said ratchetwheel and a tail end (7) away from the ratchet end (6), a through hole(8) for said shaft (3) is provided between the ratchet end (6) and thetail end (7).
 3. The clutch according to claim 2, wherein the distancefrom the tip of the ratchet end (6) to the axis of the through hole (8)is larger than that from the tip of the tail end (7) to the axis of thethrough hole (8).
 4. The clutch according to claim 3, wherein the ratioof the distance from the tip of the tail end (7) to the center of thethrough hole (8) to the distance from the tip of the ratchet end (6) tothe center of the through hole (8) is 1:1.1.
 5. The clutch according toclaim 1, wherein the clutch further includes a mounting sleeve (10)embedded in said disk member (5), the permanent magnet (4) is providedin said mounting sleeve (10).
 6. The clutch according to claim 5,wherein the mounting sleeve (10) is made of non-magnetic material. 7.The clutch according to claim 5 or 6, wherein the mounting sleeve (10)is made of stainless steel.
 8. The clutch according to claim 1, whereinthe permanent magnet (4) is made of Neodymium-Fe-Boron.
 9. The clutchaccording to claim 1 or 8, wherein the shape of the permanent magnet (4)is a cylinder and its diameter is 16 mm and its height is 10 mm.
 10. Theclutch according to claim. 1, wherein the distance between the tail end(7) of said pawl (2) and the permanent magnet (4) is 1 mm when theratchet end (6) of said pawl (2) engages with the teeth (9); the maximumdistance between the tail end (7) of said pawl (2) and the permanentmagnet (4) is 5 mm when the pawl (2) disengages with the teeth (9).